Preparation of Enantiomerically Pure 5-Palladatricyclo[4.1.0.0]heptanes and Conversion into Enantiomerically Pure Complexes with Helical Chirality at Palladium

摘要

In 1971 Maitlis observed the formation of stable palladoles 1 from Pd° compounds and acetylenedicarboxylates. In the following years the chemistry of these compounds was intensively investigated by several groups. Of special significance for organicchemists was the subsequent ob-servation made by Trost and Tanoury in 1987 that palladoles are cycloisomerization catalysts fa-cilitating unique, synthetically very interesting reac- tions (enyne metathesis and related conversions). In some of these cycloisomerization reactions racemic products with one or more stereocenters are formed from achi-ral starting compounds. While the diastereoselectivity of these reactions with regard to stereocenters already existing in the starting material has been investigated, so far no chiral catalyst has been found that enables an asymmetric induction. Our aim is the synthesis of chiral catalysts with palladole-like structure for the enantioselective variants of the reactions mentioned above. We were encouraged by successful applications of achiral palladacycles with carbon ligands as catalysts for Heck and cross-coupling reactions.